Railway traffic controlling apparatus



March 1943- L. R. ALLISON I RAILWAY TRAFFIC CONTROLLING APPARATUS Filed April 26, 1941 d R Y i x m m 0 2 b 5 v m [5 1D 0 9 m O? A P A w T ET L m C 0 0 Y. H B TQ R Imhbmb I 1 ou w L1 .m

j E W Patented Mar. 2, 1943 RAILNAY iRAFFIC CONTROLLING APPARATUS Leslie R. Allison, Forest Hills, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application April 26, 1941, Serial 399, 99

6 Claims. (01. 2 l663) My invention relates to railway trafiic controlling apparatus, and it has particular reference to apparatus of the type employed in railway signal systems wherein coded track circuit energy is employed to effect control of either or both wayside signals and train-carried trafiic controlling devices such as cab signals and train control apparatus. More particularly, my invention relates to decoding apparatus employed in such systems for decoding coded track circuit energy.

In coded systems of railway signaling, energy coded or periodically interrupted at one or another of a plurality of code rates of the frequency code type comprising recurrent cycle each consisting of one on and one off interval during which energy does and does not flow, respectively, is transmitted through the track rails to cause operation of a code following relay device which may, for example, be of the tractive armature; saturable core; or electronic tube type. In such a system, the rate of operation of the code following relay is detected by means of decoding apparatus including circuits tuned to resonance at one or another of a plurality of code rates and supplied with energy from a decoding transformer. The decoding transformer is supplied with unidirectional current during each on and off interval of the track circuit current, in such manner as to reverse the direction of flux in the decoding transformer at a rate corresponding to the rate of operation of the code following relay. This reversal of flux in the decoding transformer causes the induction in the transformer of an alternating electromotive force having a frequency corresponding to the rate of flux reversal.

The tuned circuits supplied with energy from the decoding transformer are tuned to resonance at frequencies corresponding to one or another of the code rates employed. In systems now commonly in use, code ratesof 75, 120 and 180 cycles per minute are employed, and the decoding apparatus is arranged to detect '75 code by means of an untuned circuit and the 120 and the 180 codes by means of tuned circuits selectively responsive to .one or the other of the desired code rates. The selectivity of these tuned circuits of course varies in accordance with the frequency of current supplied thereto, with the result that certain harmonics of the low (7 code rate might fall within the range where the tuned circuits are less selective. Similarly, harmonics of the intermediate (120) code rate might be objectionable from the standpoint of the selectivity of the circuits.

The decoding apparatus employed in railway signal systems is required to meet certain specified standards based upon safety of operation, size, weight, shape, and other factors. These limitations make it essential that the size and the weight of the apparatus be kept always at a minimum, thereby limiting the size of the ma netic core structure employed in the decoding transformer and tuning reactors. As a result, therefore, the apparatus must ,be designed around a given sizecore structure with the windings and. tuning apparatus proportioned with respect to the core. The inductance to resistance ratio of the windings of the decoding transformer is, therefore, limited since a relatively high ratio results in early saturation of the core due to the ampere turns available. To avoid such saturation, a lower ratio of inductance to resistance is employed, and as a result the energy supplied to the transformer has a substantially square-cornered wave form, and the variations of flux in the transformer have a similar form. At the '75 code rate, and to some .c ent also at the code rate, the e1ectromotive fo ces ind e in the transformer comprises sharply peaked impulses separated by intervalswhen little or no voltage is induced. In the tuned circuits, these impulses act as though comprised of ,a fundamental frequency richin harmonics. The harmonic portion of such voltages, lying within the less selective portions ,of the resonant curves of the tuned circuits, causes ,a.,current t0 fiQW therein relatively higher in magnitude thanih d e t th fu d mental frequ ncy of the low Code rate. This then decreases to a con de ab e ex en the seiectivity of the rcuits and mi lowe the a i O safety of the circuits to a large extent.

With the size of the core limited, and with restrictions placed .upon the inductance-resistance ratio ,of the windings, other means must be devised to yarythewave formof flux in the transformer so as to approx mate ore close a sinusoidal wave form to which the tuned circuits are mostselective. An object .ofmy invention is the provision .of decoding apparatus incorporating novel and improved means for obtaining anoutput voltage wave substantially sinusoidal in form and having relativelylowharmonic components.

Another object is to provide decoding apparatus arranged to delay the growth and decay of flux in adecoding transformer whereby to cause the resultant induced v,o ltage to-have relatively ow harmonic comp nen s A furt e object is o p ovide d od n pparatusmeeti allthe equir m n o r i w ysisnal ns as to s ze, s ap w i t, et n inca porating novel and improved means for increasing the selectivity of the tuned circuits forming a part thereof.

The above-mentioned and other important objects and characteristic features of my invention which will become readily apparent from the following description, are attained in accordance with my invention by incorporating into the decoding apparatus reactance devices so arranged as to delay the growth and decay of flux in the decoding transformer, or in other words, to increase the time constant of the circuit which includes the primary winding of the decoding transformer. This reactance unit may take the form of a copper ferrule, or a short-circuited winding mounted on the transformer core.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a diagrammatic view illustrating a preferrred form and arrangement of apparatus embodying my invention. Fig. 2 is a graph in which the time rate of change of flux in an ordinary decoding transformer and a decoding transformer constructed in accordance with my invention are represented by curves a and b, respectively. Fig. 3 is another graph representing the resultant induced voltages in the transformers. Fig. 4 is a graphical representation of the selectivity curves of decoding apparatus constructed in accordance with the usual practice and also in accordance with my present invention.

In' the particular embodiment of my invention illustrated in Fig. 1, apparatus embodying my invention is shown applied to a four-indication cab signal system wherein selective control of a traincarried cab signal is established in accordance with the rate at which energy inductively received from the rails of a trackway is coded. Referring now to Fig. l, the reference characters I and ia designate the track rails of a stretch of trackway, the rails of which are supplied with track circuit energy coded at one or another of the customary plurality of code rates. The wayside apparatus which supplies coded energy to the rails l and la. is not shown in the drawing since it forms no part of my present invention, but such apparatus may take any one of the wellknown forms employed in what is known as three block, four-indication frequency code signal systems, effective to supply the rails of the trackway with energy which is coded at one or another of three different rates of coding in accordannce with trafiic conditions in advance, For the purposes of this description, I shall assume that the rails l and la are supplied by such wayside apparatus with alternating trackway energy which is coded or periodically interrupted at a rate of 75, 120 or 180 times per minute. In accordance with the usual practice, I shall assume that the wayside apparatus is controlled by traffic conditions in advance so that the highest or 180 code rate is supplied to the rails l and la under clear traffic conditions on the stretch; that the intermediate or 120 code is supplied under approach medium traffic conditions; and that the induced therein in response to alternating currents of opposite instantaneous polarities in the rails l and la, such forces are additive. The two coils l and 5 are connected through the mediumof the usual amplifier AM to a master code following relay MR.

The reference characters L, R. and A designate decoding relays for detecting the rate of operation of code following relay MR, and which decoding relays may be utilized as shown for controlling a train governing device such as a cab signal CS. In accordance with the usual custom, the apparatus is arranged so that when relay A is energized, lamp 8 of signal CS is illuminated to indicate a clear traffic condition; when relay A is released and relay R is picked up, lamp 9 is illuminated to indicate an approach medium traffic condition; when relays A and R are released and relay L is picked up, lamp I0 is illuminated to indicate an approach trafiic condition; and when relays A, R and L are released, lamp H is energized to indicate slow speed.

The decoding relays are selectively controlled by relay MR in accordance with its rate of operation through the medium of decoding apparatus comprising selective circuits and a decoding transformer DT. Transformer DT comprises a magnetizable core upon which are mounted a primary winding [5 and a secondary winding l5. One terminal C of a suitable source of unidirectional current, such as a battery not shown but having its opposite terminals designated by the reference characters 13 and C. is connected through a resistor It to a mid terminal tap of winding i i, and the other terminal B of the source is connected to one end or the other of winding it according as contact I l of relay MR is in its attracted front position or is in its released back position, respectively. As shown, a condenser |8 may be connected across winding [4 to suppress sparking at the contacts of relay MR. It follows, therefore, that the flux in the core of transformer DT is reversed at a rate correspond-. ing to the rate of operation of contact I! of master relay MR.

Relay L is connected through a ful1-wave rectifier l9 and a reactor 29 to secondary winding l5 of transformer DT, and this relay, as will be made clear presently, is picked up whenever relay MR follows any one of the heretofore mentioned code rates of 75, 12c and 180 cycles per minute.

Relay R is connected through a full-wave rectifier E9 to a secondary winding 2! inductively coupled with a reactor winding 22 connected in series with a capacitor 23 across winding l4.of transformer DT. Relay R, as will be made clear presently, is effectively energized and picked up when relay MR operates at the code rate. The other decoding relay A is connected through a full-wave rectifier Hi to a secondary winding 24 inductively coupled with a reactor winding 25, which latter winding is connected in series with a capacitor 25 across winding [4 of transformer DT. Relay A is effectively energized and picked up when and only when relay MR operates at the code rate. The parts of the apparatus are proportioned in such manner that the circuit path including capacitor 23 and reactor winding 22 is tuned to resonance at a frequency (2 cycles per second) corresponding to the 120 code rate, while the other circuit path comprising capacitor 26 and reactor winding 25 is tuned to resonance at a frequency (3 cycles per second) corresponding to the 180 code rate.

The apparatus so far described corresponds to that-heretofore proposed and such apparatus functions in thev following manner. When 75 code energy is inductively received by the coils Q and 5. r l y operates at the 75 c e r t o cause flux reversals in the transformer DT to occur at a corresponding rate. Due to the heret fore m ntioned limitations upon the size ofcore and ;inductance-resistance ratio of the transo m r. t f ux bui ds up qui k y in the core each time contact ll of relay operates from one pos t on t he th The .fi-ux growth in the core of transformer DT at the 75 code rate is represented by curve a of Fi ,2, and it is readily apparent from an inspection of this curve that the time (A) required for the flux to build up to its maximum value is substantially less than either the on or "off interval time (OA) of the '75 code. The resultant voltage induced in transformer winding l by this flux variation is represented in curve ,a of Fig. 3, and from an inspection of this curve it is readily apparent that the voltage induced is of relatively short duration and is sharply peaked. Voltage impulses corresponding to those shown in curve a of Fig. 3 occur each time contact I! of relay MR operates from one position to the other, it being understood of course that each two successive impulses have opposite polarities. These impulses are applied from winding l5 through rectifier I 9 to relay L in the form of impulses of unidirectional current, and relay L accordingly is energized. The circuit connection of relay L to winding :5 of transformer DT is untuned, hence such relay is energized by voltage impulses occurring at any one of the heretofore assumed code rates of 75, 120 and 180 cycles per minute. At the higher code rates, the spacing between voltage impulses is of course decreased and the energization of the relay L is increased. To avoid overenergizing relay L at the higher code rates, reactor 20 is introduced in the circuit of relay L to limit the applied voltage, and is proportioned so as to maintain substantially constant the energization of relay L irrespective of the code rate of operation of relay MR.

The impulses of voltage induced in transformer DT are applied also to the selective circuits, but since these impulses occur at the 75 code rate and the circuits are tuned at 120 and 180 code rates, respectively, little current flows in the circuits due to the fundamental frequency of the '75 code. However, the separation between impulses permits the harmonic content thereof to cause the resonant circuits to oscillate at their natural periods with the result that an appreciable current flows, as indicated in curve a of Fig. 4, wherein the current values caused to be induced in winding 24 are plotted on a logarithmic scale against code rates. Curve a of Fig. 4 accordingly represents the energization of relay A at the different code rate of operation of relay MR. Relay R also has an appreciable energization at the 75 code rate due to the harmonic content of the voltage impulses occurring at the 75 code rate.

In accordance with an object of my invention, I modify the decoding apparatus heretofore described by incorporating therein a reactance device eifective to reduce the harmonic content of the induced voltages applied from the transformer to the selective circuits. This reactance device may take the form of a copper ferrule mounted on the core of the decoding transformer, or as represented in Fig. 1, the device may be a winding 21 disposed on the transformer core and comprising a relatively few turns of heavy wire, for low resistance. The winding 2] is short-circuited upon itself, and by suitably proportioning winding 21, the time constant of the transformer may be adjusted so as to obtain a delay in both the growth and decay of flux in the transformer and cause the time rate of change of flux to vary substantially as shown in curve b of Fig. 2. The voltage induced in winding l 5 of the transformer by this rate of flux change has a wave form substantially similar to that represented in curve 12 of Fig. 3, and from an inspection of this curve it is evident that the induced voltage wave contains a much greater proportion of the fundamental frequency of '75 cycles per minute than does the voltage curve a of Fig. 3. As a result, an electromotive force is impressed on the resonant circuits throughout substantially the entire code on and off intervals of the 7.5 rate, and the circuits accordingly are less free to oscillate at their natural frequencies in response to the harmonic components of the induced voltages. Also, the harmonic components of the induced voltages are reduced and the current available in the tuned circuits at the 75 code rate is thus reduced in magnitude, as can be seen from an inspection of curve 12 of Fig. 4.

The short-circuited winding 21 of the transformer of course absorbs power, and the magnitude of this power is proportional to the frequency. I have found that at the higher rates and cycles per minute) the power absorbed by winding 21 (or its equivalent copper ferrule) tends to offset the increased power available to energize the untuned relay L, with the result that the energization of such relay is maintained substantially constant over the range of code rates employed. This permits reactance 20 interposed in the circuit of relay L to be reduced considerably, thereby effecting a saving in apparatus. Similarly, in case rectifier I9 is elimihated and the untuned relay L is supplied over a contact of master relay MR with substantially unidirectional current from its associated secondary winding IS in a manner disclosed in United States Letters Patent No. 2,237,788, granted on April 8, 1941, to Frank H. Nicholson and myself and of common ownership herewith, the winding 2! functions to maintain substantially constant the energization of relay L without the use of a reactor.

I have also found that the selectivity of the tuned circuits at their resonant frequencies is substantially unchanged when winding 21 is incorporated into transformer DT. An inspection of curve 5 of Fig. 4 reveals that at the resonant frequency (180 code rate) the current induced in winding 25 and made available in relay A is substantially the same irrespective of whether winding 2? is or is not utilized, but as the code rate decreases, considerably more energy is available when winding 27 is not employed (curve 11) than is available when the winding is used (curve 1)). The short-circuited winding 21, or copper ferrule, may thus be considered as giving transformer DT the characteristics of a low pass filter having a cut-off point such that it does not pass the harmonies of the 75 code, corresponding to 225, 375, 525, etc., cycles per minute, to which frequencies the tuned circuits of the A and R relays are readily responsive. It follows, therefore, that I have provided decoding apparatus incorporating novel and improved means for increasing the selectivity of tuned circuits of the type employed in coded railway signal systems, and have enabled such gain in selectivity to be obtained without increasing the size or weight of the magnetizable core employed in the apparatus.

In addition, apparatus embodying my invention is effective to limit the energization of the untuned relay L and thus maintain substantially constant the energization of the relay over the range of code rates employed. This enables the limiting reactor introduced into the untuned cirouit of the 75 code to be greatly reduced or entirely eliminated, thereby reducing the number of elements required in the decoding apparatus.

An additional advantage of apparatus embodying my invention resides in minimizing the possibility of false clear failures due to an opencircuit condition in the untuned circuit of relay L. This possibility exists when, as has been the practice heretofore, a relatively large reactor is introduced in the L relay circuit to prevent overenergization of the relay at the higher code rates, since the voltage impressed by the transformer on the circuit must be relatively high in order properly to energize the relay at the low ('75) code rate. This of course means that a relatively large proportion of the transformer power is required to operate relay L. The circuit of this relay is not checked, hence should an open-circuit condition exist therein, the energy available at the 75 code rate to energize the tuned circuits of the A and R. relays is increased due to the regulation of the transformer, and at the '75 code rate, the current in the tuned circuits might reach a value sufficient to prevent either, or both, the A and R relays from dropping away. Similarly, if the L relay circuit is open at the 120 code rate, relay A might be prevented from dropping away. My invention, by enabling a much smaller reactor to be employed in the untuned circuit of relay L, permits operation of the relay to be obtained with a lower impressed voltage from the transformer and less transformer power. I have found that if the untuned circuit of relay L becomes open-circuited at the 75 code rate, the energy available to energize the tuned circuits of the A and R relays, due to the regulation of the transformer, is much less when apparatus embodying my invention is employed than that available when apparatus of the type heretofore in common use is employed. It follows, therefore, that apparatus embodying my invention minimizes the possibility of false clear failures such as might be caused by an open-circuit condition in the untuned circuit of the L relay.

It is, of course, to be understood that although my invention has been described in connection with train-carried apparatus, the invention may be applied equally as well to wayside apparatus incorporating decoding apparatus for decoding coded track circuit energy.

Although I have herein shown and described only one form of railway trafiic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Decoding apparatus for use in railway signal systems having a code following relay responsive to track circuit energy coded at one or another of a plurality of code rates each rate comprising recurrent cycles consisting of alterhate on and off intervals during which ene'rgy is and is not present in the track rails, comprising the combination with said code following relay of a decoding transformer having a magnetizable core provided with a winding supplied by said relay with unidirectional current in such manner as to cause reversals of flux in ,the transformer at a rate corresponding to the code rate of operation of said relay, selective circuits tuned to resonance at one or another of the plurality of code rates and supplied with energy from a winding of said transformer, and reactivemeans associated with said transformer for delaying the growth and decay of flux therein to reduce the harmonic components of voltages applied from the winding of said transformer to said selective circuits and thereby improve the selectivity of such circuits.

2. Decoding apparatus for use in railway signal systems having a code following relay responsive to track circuit energy coded at one or another of a plurality of code rates each rate comprising recurrent cycles consisting of alternate on and off intervals during which energy is and is not present in the track rails, comprising the combination with said code following relay of a decoding transformer having a magnetizable core provided with a winding supplied by said relay with unidirectional current in such manner as to cause reversals of flux in the transformer at a rate corresponding to the code rate of operation of said relay, selective circuits tuned to resonance at one or another of the plurality of code rates and supplied with energy from a winding of said transformer, and a short-circuited winding mounted on said transformer core for delaying the growth and decay of flux therein to reduce the harmonic components of voltages applied from the winding of said transformer to said selective circuits and thereby improve the selectivity of such circuits.

3. Decoding apparatus for use in railway signal systems having a code following relay responsive to track circuit energy coded at one'or another of a plurality of code rates each rate comprising recurrent cycles consisting of alternate on and ofi intervals during which energy is and is not present in the track rails, comprising thecombination with said code following relay of a decoding transformer having a magnetizable core provided with a winding-supplied by said relay with unidirectional current in such manner as to cause reversals of flux in the transformer at a rate corresponding to the code rate of operation of said relay, selective circuits tuned to resonance at one or another of the plurality of code rates and supplied with energy from a winding of said transformer, and inductive means comprising a short-circuited turn mounted on said transformer core for delaying the growth and decay of flux therein to reduce the harmonic components of voltages applied from the winding of said transformer to said selective circuits and thereby improve the selectivityof such circuits.

4. In combination with a code following relay operable by track circuit energy coded at one or another of a plurality of code rates, each rate comprising recurrent cycles consisting of an on and an off interval during which energy is and is not present, a decoding transformer having a magnetizable core provided with a winding supplied by said relay with unidirectional current flowing therein in one direction during the on" intervals of code and flowing in the opposite direction during the off intervals of code, selective circuits tuned to resonance'at one or another frequency corresponding to one or another of said plurality of code rates, means for supplying said circuits with energy from a winding of said transformer, and a short-circuited turn on'said transformer core for increasing the time constant of said transformer to reduce the harmonic content of energy applied from said transformer to said circuits, whereby to increase the selectivity of such circuits.

5. Decoding apparatus for use in railway signal systems having a code following relay operable by track circuit energy coded at 75 and 180 cycles per minute, each cycle comprising an on and an off interval when energy is and is not present, comprising the combination with said relay of a decoding transformer having a magnetizable core and a winding supplied by said relay with unidirectional current flowing in one direction therein during each on interval of a code and flowing in the opposite direction therein during each off interval of the code, a selective circuit tuned to resonance at a frequency of three cycles per second and supplied with energy from a winding of said decoding transformer, and a short-circuited turn inductively associated with said first-mentioned winding of said transformer for reducing the harmonic components of the voltages applied from the transformer to said selective circuit when said relay operates in response to 75 code track circuit energy.

6. In a system for decoding coded track circuit energy of the class wherein a code following relay operated by track circuit energy supplies energy to a decoding transformer for causing alternating current having a frequency corresponding to the code rate of operation of the relay to be supplied to a circuit tuned to resonance at a frequency corresponding to one of the relatively high code rates and to an untuned circuit including a reactor for limiting the energization of the untuned circuit at said one rate, the improvement of minimizing the possibility of overenergizing the tuned circuit at a lower code rate, comprising the provision on the decoding transformer of a short-circuited turn and the reduction in size of the limiting reactor in the untuned circuit, for limiting the energization of the untuned circuit jointly by the reactor and shorted turn and reducing the power required to be supplied to the untuned circuit from the transformer, whereby to avoid overenergizing the said tuned circuit at the lower code rate should an open-circuit condition exist in said untuned circuit.

LESLIE R. ALLISON. 

